1. Field of the Invention
The invention relates to a bone anchoring device including a bone anchoring element and a receiving part for connecting the bone anchoring element to a rod. The head of the bone anchoring element is locked in the receiving part by compression of a portion of the receiving part laterally surrounding the head by means of a locking ring, which is pressed down by the rod. The locking ring has two upwardly extending projections that extend into the channel for the rod and can be engaged by the rod to exert pressure onto the locking ring. The upwardly extending projections cooperate with the receiving part in such a way that the locking ring can assume a position in which the head is pivotable in the head receiving portion but can not be removed from the head receiving portion.
2. Description of Related Art
A bone anchoring device which includes a bone anchoring element and a receiving part with a rod receiving portion and a head receiving portion and a locking ring for locking the head in the head receiving portion is known from EP 2 022 423 A1. Below the bottom of the channel for the rod in the rod receiving portion cutouts are provided on either end of the channel, through which two upwardly extending projections of the locking ring extend into the channel, so that they are engageable by the rod. In one embodiment, the upwardly extending projections have lateral projections which snap into the channel to prevent the locking ring from falling off when the head is not inserted into the head receiving portion.
WO 2007/038350 A2 describes an apparatus for connecting a bone anchor to a support rod, the apparatus including a connector body and a cap. The connector body has a channel to receive and locate the support rod relative to the bone anchor. A sleeve fits over a socket portion of the connector body in a temporary position, in which the sleeve permits insertion of the bone anchor into the socket. The sleeve can then be moved to a provisional locking position, in which the sleeve permits angulation but prevents removal of the bone anchor and can further be moved to a locking position in which the sleeve prevents both angulation and removal of the bone anchor.